Method and apparatus for pneumatically discharging a drum centrifuge

ABSTRACT

A continuously operating filter centrifuge is automatically discharged and the discharged product is dried within the pneumatic conveyance system. The solvent vapors are reclaimed through condensation from the inert carrier medium which is recirculated. The gas-tight circulation system begins and ends at the centrifuge and thus avoids any noticeable losses in either product, or solvent, or nitrogen. It makes possible the elimination of the oxygen surveillance, previously needed to provide safety against explosions.

Tlite States Patent 1 1 3,763,572

Titus Get. 9, 1973 METHOD AND APPARATUS FOR 2,691,830 1954 Karnofsky 34/75 PNEUMATICALLY DISCHARGING A DRUM 2,663,089 12/1953 Coats 34/75 CENTRIFUGE 2,409,713 10/1946 Sharples 34/69 2,198,412 4/1940 McDonald 34/8 [76] Inventor: Hans-Joachim Titus,

Von-Hees-Strasse 5,

fleppenheim/Bergstrasse, Germany Przmary Examiner-Kenneth W. Sprague Assistant Examiner-James C. Yeung [22} Filed: June 9, 1971 Attorney-Arthur Schwartz [21] Appl. No.2 151,231

[57] ABSTRACT Foreign Application Priority Data June 9 1970 Germany P 20 28 267 l A cont nuously operating filter centrifuge 1s automativ cally discharged and the discharged product 15 d i U 8 Cl 34/58 34/60 34/69 within the pneumatic conveyance system. The solvent 34/79 vapors are reclaimed through condensation from the lm CI F26) 17/24 inert carrier medium which is recirculated. The gas [58] Field o'r's'i'c'ii'fIffffffIIfffffffffff 3 1714, 8, 11, 17, tight system begms and ends fuge and thus avoids any noticeable losses in either 34/58 72 80 233/1 1 product, or solvent, or nitrogen. It makes possible the elimination of the oxygen surveillance, previously [56] References Cited needed to provide safety against explosions.

UNITED STATES PATENTS 3,268,078 8/1966 Muggli 233/11 10 Claims, 7 Drawing Figures t g 33 I 16 l 17 QT'J l3 l 36 I ll 10 1 .15 i r i'lg f n L J;

PATENTEB 9 m5 ShEET 3 UP 5 IN VENTOR.

HANS-JOACHIM TITUS PAHN IEU 9 5 INVEN TOR.

HANS-JOACHLM TITUS PAILNIEU 91955 SHEU 5 BF 5 wdI m 0 Q8 N 8 INVENTOR.

HANS-JOACHIM TITUS METHOD AND APPARATUS FOR PNEUMATICALLY DISCHARGING A DRUM CENTRIFUGE BACKGROUND OF THE INVENTION 1. Field of the Invention The invention relates to methods and apparatus for discharging solid material from centrifuges, and in particular to a method and apparatus for pneumatically discharging a drum centrifuge.

1. Description of the Prior Art In the process of fabricating pharmaceutic or other products, the suspension which has been prepared in agitator vats must be separated by means of a centrifuge into solid matter on the one hand and liquour on the other hand. The vertical type of drum centrifuge with top discharge was found to be suitable for this purpose. In this case, however the operator must perform several successive operations. They are: a) opening and closing of the vat discharge, b) supervision of the transfer into the centrifuge, c) washing of the product, d) monitoring of the duration of centrifuge operation, e) shut-down of the centrifuge and opening of the centrifuge cover, and f) removal of the product with a shovel. In cases where the product has been prepared with a solvent and is then required to be washed, the operator is exposed to potentially hazardous vapors.

It has therefore been already suggestedto provide suction exhaust systems, but the latter require about as much energy as the centrifuge procedure itself. In spite of this improvement, the operator in most cases must protect himself from the vapors by means of a gas mask. Additional shortcomings are that the removal of the product by shovelling is tiresome, the filter fabrics can be easily damaged, and this'discharge operation takes at least the same amount of time again as the complete loading procedure. Further time is lost through the need for scavenging the centrifuge with nitrogen, in order to remove any danger of explosion. These extended charge intervals make a continuous drying process impractical. It is therefore necessary to use for this purpose vacuum-operated, complex drying equipment which operates intermittently and whose drying cycle frequently requires hours of drying time. Transfer of the product from the storage container to the drying apparatus again requires a tiresome operation. The vacuum in the drying apparatus is produced by water ring pumps, and the latter tend to liquify the solvent vapors, carrying them into the used water system. By this process, the biological need for oxygen in the water is increased and the capacity of the purification system is correspondingly reduced.

The present invention represents a developmental improvement over applicants U.S. Pat. No. 3,474,905.

SUMMARY OF THE INVENTION The invention, in order to reduce and overcome the above mentioned shortcomings, addresses itself to the following objectives:

1. A reduction in the amount of physical'work required;

2. A reduction in the time required for loading;

3. An operation which has a gas-tight, closed circulatory system;

4. The elimination of contamination and of any losses of either product, solvent or carrier medium;

\ pensive vacuum drum dryers;

9. Elimination of any pollution of the used water and air;

l0. Proposal of a special condenser apparatus for nitrogen solvents; and

l l. Elimination of the oxygen surveillance in the case of a nitrogen cover.

The invention therefore suggests a pneumatic discharge method and apparatus where the discharge operation is automatically and precisely controlled and where the removed product is immediately dried and separated, while the entire amount of solvent used is reclaimed. The discharge device itself is preferably an explosion-proof structure, so that the use of flammable solvents does not require the previously necessary expensive oxygen monitoring system.

The invention thus suggests a discharge apparatus in combination with a gas-tight centrifuge housing which contains a scraper head movably arranged therein, including means to control the position of the discharge pipe. It further includes a suction pipe which communicates with the discharge pipe in a telescopic joint, a gas circulation pump with a product separator arranged ahead of the pump. The device thus presents a closed circulatory system, whereby the gas circulation pump communicates on the one side, via a condenser and an upstream heater, with the housing of the centrifuge, while on the other side it leads, via a product separator and a drying line, to the suction pipe of the discharge device.

BRIEF DESCRIPTION OF THE DRAWINGS The characteristics and advantages of the invention and the construction of the individual parts of the new device and method will be described in more detail with reference to several preferred examples of the invention, as explained with the help of the accompanying drawings, in which:

FIG. 1 shows a schematic layout of a circulatory discharge system representing an embodiment of the invention;

FIG. 2 shows a modified portion of the embodiment represented in FIG. 1;

FIG. 3 shows the portion of FIG. 2 in a further modification;

FIG. 4 represents a vertical cross-section through a condenser apparatus as used in the circulatory system of the invention;

FIG. 5 represents a horizontal cross-section through the condenser apparatus of FIG. 4; and

FIG. 6 shows in an i,x-graph the ratios between acetone and nitrogen;

FIG. 7 shows in an i, x-graph the ratios between methanol and nitrogen.

DESCRIPTION OF THE PREFERRED EMBODIMENTS As can be seen in FIG. 1, the cover 10 of a centrifuge 11 carries a scraper housing 14 inside which is mounted on a rotatable and height-adjustable discharge tube 12 therefor having a scraper head 112a, the discharge tube in turn therefor being telescopically guided inside a stationary suction pipe 13. The fact that the discharge tube 12 is rotatable with respect to the suction pipe 13 and the further fact that the tube 12 and pipe 13 are offset from the central axis of the centrifuge, results in a device whereby rotary movement of the discharge tube 12 effects a change in the radial position of the scraper head 12a with respect to the centrifuge. The suction pipe 13 leads to a drying line 31. The fact that the discharge pipe 12 is guided clearance-free and its radial and axial adjustments are controllable to a high accuracy makes possible the peeling of very thin product layers from the centrifuge to facilitate the drying of the product. The scraping operation is controlled automatically by means of hydraulic drives and electric end switches.

The solid matter (product) which remains inside the drum I5 is peeled off the drum wall at speeds of 50-200 rpm and removed pneumatically. The dried product is separated from the conveying gas in a cyclone separator 32, from where the conveying gas is forced back into the centrifuge 11 by means of a blower 33. After passing through the heater 35 (heat exchanger), the carrier medium enters into the centrifuge housing where it entrains the product which is continuously being peeled from the drum, conveying it through the drying line 31. The carrier gas, after the product has been removed in the cyclone separator, remains enriched with solvent when it passes through the high pressure blower into a condenser apparatus 34. In cases where a fine-grain product is being processed, it may be advisable to arrange a tube filter between the cyclone separator and the blower. The condenser has the purpose of removing the solvent from the carrier gas, thereby restoring to the carrier gas its capacity to absorb the solvent which is released from the peeled off product during the process. After leaving the condenser, the carrier gas is reheated in the heat exchanger 35 from where it passes back into the centrifuge.

In FIGS. 2 and 3 are shown two different versions of gas conduit systems, adapted to varying temperature sensitivities of different products. The system part shown in FIG. 2 is suitable for comparatively wet products with a tendency of caking to the walls, while FIG. 3 shows a version suitable for the conveyance of temperature sensitive products. In both cases, the additional line 37 represents a bypass line with respect to the pressure line 36 which leads into the centrifuge, conveying heated carrier gas in the case of FIG. 2, while conveying cold carrier gas in the case of FIG. 3.

The drying operation can be laid out and calculated by referring to the graphs shown in FIGS. 6 and 7 which represent i,x-graphs for two conventional solvents, using nitrogen as a carrier medium. In these graphs, the drying triangle represents the following changes in physical state:

I: Gas state between the condenser and the heat exchanger (original state: x 1.0; gas saturated) I II: Heating of the gas;

II: Gas state at the exit from the heat exchanger (begin of drying process);

II-III: Drying at constant enthalpy;

III: Gas state between the cyclone separator and the condenser. Ifthe line II-III is extended to the vapor saturation line, one obtains the cooling limit temperature. This means that a substance does not increase in its temperature as long as it still contains humidity;

III-I: Condensation.

The distance AX on the abscissa shows the evaporated and reclaimed amount of solvent per kilogram of nitrogen. The solvent content of the gas in the original state (I) can be fixed at random. The invention suggests that this point be fixed in such a way that it is always situated about the ignition range, so as to offer the following cost saving advantages:

a. The solvent vapors are not ignitable in air; the costly oxygen surveillance is no longer necessary;

b. The high content of solvent in the gas facilitates condensation; and

c. The required condenser surface is reduced because of the high average temperature differential.

It thus becomes apparent that the condensation process is of crucial importance. The reliability of the entire device is dependent upon the efficiency of the condenser.

As can be seen in FIG. 4, the condenser 34 of the invention includes several condensation zones, thereby precluding any contamination, while preventing the undesirable formation of an insulating film of condensate on the cooling pipes. The condenser 34 of FIGS. 4 and 5 has an elongated housing with connecting flanges and 41 on its ends. The cooling surfaces are formed by pipes 43 which have a flattened cross-section and through which flows the coolant in a counter current. The cooling pipes are arranged in groups in upright orientation, forming an angle of approximately 45 to the longitudinal center axis of the condenser. The cooling pipes are welded into upper and lower pipe panels 49 and 50 which represent the upper and lower boundaries of the gas flow channels 43. Between the pipe panels and the wall of the condenser housing 42 are arranged baffle panels 51 which guide the flow of the coolant cross-wise and in opposite direction to the flow direction of the gas. The lateral exterior cooling surfaces, together with the guide panels 45, form flow channels 44 for the gas, giving it a zigzag" flow pattern.

Each cooling pipe includes on its downstream end a separator lip 47 which collects the condensate as well as the residual dust. The shape of the separator lip is such that it creates a low pressure zone which facilitates the removal of the condensate. From the lower end of each of these curved separator lips 47, extends a pipe 52, as shown in the plan view of FIG. 4. This pipe 52 extends from the condenser housing 42 into a solvent-containing receptacle 54, in order to prevent any bypass flow of the gas which could be caused by the pressure differential of approximately 300 Torr. over the length of the condenser. The gas flow speed of between 6 and 15 m/s determines the cross-section of the condenser as well as the required cooling surface and thus the number of pipe groups. When using acetone as a solvent, for example, it is suggested to use eight pipe rows in the condenser. Due to the effect of the separating zones at the end of each cooling surface, the gas enters each subsequent cooling pipe group free of droplets, and at the end thereof it is again freed of droplets and residual dust.

In the pressure line 36 (FIG. 1) immediately following the blower is also arranged a drainage valve 16 together with an outlet 17. Further downstream behind the valve 16 is arranged an intake line 18 for inert gas which is used to scavenge the air contained in the circulation system prior to the start-up of operation.

While the invention has been described, it will be understood that it is capable of further modifications and this application is intended to cover any variations, uses or adaptations of the invention following in general the principles of the invention and including such departures from the present disclosure as come within known or customary practice in the art to which the invention pertains, and as may be applied to the essential features hereinbefore set forth and as fall within the scope of the invention or the limits of the appended claims.

I claim:

1. A device for pneumatically discharging solid matter from a drum centrifuge comprising in combination:

a gas-tight housing for the centrifuge;

a gas-tight closed-circuit conduit system originating and terminating inside the centrifuge housing for circulating a contained carrier medium; the conduit system comprising:

means for forcibly circulating the carrier medium;

means for scraping from the drum of the centrifuge a layer of solid matter to be conveyed into the conduit system by the carrier medium;

means for evaporating from the scraped-off solid matter the residual humidity during conveyance inside the conduit system;

means for separating the solid matter from the carrier medium;

a receptacle in the conduit system for collecting separated solid matter; and

means for separating and collecting from the carrier medium the humidity previously evaporated from the solid matter.

2. The device as defined in claim 1, wherein the evaporating means includes a heater for the carrier medium to permit heat-drying of the solid matter during conveyance inside a portion of said conduit system downstream of the drum centrifuge.

3. The device as defined in claim 2, wherein the heater is arranged upstream of the centrifuge housing, the heated carrier medium passing through the centrifuge.

4. The device as defined in claim 2, wherein the heater is arranged upstream of the centrifuge housing,

the portion of said conduit system between the heater and the centrifuge including a bypass conduit leading to a portion of said conduit system downstream of the centrifuge so that only a portion of the heated carrier medium passes through the centrifuge.

5. The device as defined in claim 2, wherein the portion of said conduit system upstream of the centrifuge housing includes a bypass conduit leading to a portion of said conduit system downstream of the centrifuge scraping means, the heater for the carrier medium being arranged in the bypass conduit, so that the heated carrier medium bypasses the centrifuge.

6. The device as defined in claim 1, wherein the scraping means includes a scraper housing mounted on the centrifuge housing, a movable discharge tube extending from the scraper housing into the drum of the centrifuge, a scraper head attached to the discharge tube and movable with the latter radially and axially relative to the drum, and a stationary suction tube with a telescopic connection to the movable discharge tube, the suction tube continuing downstream into the conduit system.

7. The device as defined in claim 1, wherein the solid matter separating means includes a cyclone-type separator and collection bunker in the conduit system downstream of the portion of said conduit system where the solid matter is dehumidified.

8. The device as defined in claim 1, wherein the humidity separating means includes a condenser arranged between the solid matter separating means and the centrifuge housing, the condenser including:

an elongated condenser housing with an intake and outlet for the carrier medium as well as an independent intake and outlet for a coolant fluid;

a plurality of substantially vertical coolant pipes of flattened cross-section arranged inside the condenser housing, the carrier medium passing horizontally between the vertical coolant pipes; and

a vertical separator lip at the downstream extremity of each coolant pipe, the separator lip having a curved profile to catch the droplets of condensate forming in the passing carrier medium.

9. The device as defined in claim 8, wherein the coolant pipes are arranged in groups of parallel pipes with flow channels therebetween, the pipe groups being mounted in upper and lower pipe panels located at a distance from the respective condenser housing walls; the condenser further including baffle panels arranged alternately between the upper and lower pipe panels and the adjacent condenser wall, thereby causing an alternately rising and falling flow of coolant through the successive groups of coolant pipes.

10. A method of discharging and processing the solvent-prepared solid matter from a drum centrifuge including the steps of:

scraping from the centrifuge drum a thin layer of solid matter;

passing a hot stream of carrier gas through the centrifuge to convey the scrapings of solid matter out of the centrifuge;

drying the solid matter during conveyance through evaporation of its solvent residue;

collecting the dried solid matter from the flowing carrier gas; and

cooling the mixture of solvent vapor and carrier gas to reclaim the solvent as condensate. 

1. A device for pneumatically discharging solid matter from a drum centrifuge comprising in combination: a gas-tight housing for the centrifuge; a gas-tight closed-circuit conduit system originating and terminating inside the centrifuge housing for circulating a contained carrier medium; the conduit system comprising: means for forcibly circulating the carrier medium; means for scraping from the drum of the centrifuge a layer of solid matter to be conveyed into the conduit system by the carrier medium; means for evaporating from the scraped-off solid matter the residual humidity during conveyance inside the conduit system; means for separating the solid matter from the carrier medium; a receptacle in the conduit system for collecting separated solid matter; and means for separating and collecting from the carrier medium the humidity previously evaporated from the solid matter.
 2. The device as defined in claim 1, wherein the evaporating means includes a heater for the carrier medium to permit heat-drying of the solid matter during conveyance inside a portion of said conduit system downstream of the drum cenTrifuge.
 3. The device as defined in claim 2, wherein the heater is arranged upstream of the centrifuge housing, the heated carrier medium passing through the centrifuge.
 4. The device as defined in claim 2, wherein the heater is arranged upstream of the centrifuge housing, the portion of said conduit system between the heater and the centrifuge including a bypass conduit leading to a portion of said conduit system downstream of the centrifuge, so that only a portion of the heated carrier medium passes through the centrifuge.
 5. The device as defined in claim 2, wherein the portion of said conduit system upstream of the centrifuge housing includes a bypass conduit leading to a portion of said conduit system downstream of the centrifuge scraping means, the heater for the carrier medium being arranged in the bypass conduit, so that the heated carrier medium bypasses the centrifuge.
 6. The device as defined in claim 1, wherein the scraping means includes a scraper housing mounted on the centrifuge housing, a movable discharge tube extending from the scraper housing into the drum of the centrifuge, a scraper head attached to the discharge tube and movable with the latter radially and axially relative to the drum, and a stationary suction tube with a telescopic connection to the movable discharge tube, the suction tube continuing downstream into the conduit system.
 7. The device as defined in claim 1, wherein the solid matter separating means includes a cyclone-type separator and collection bunker in the conduit system downstream of the portion of said conduit system where the solid matter is dehumidified.
 8. The device as defined in claim 1, wherein the humidity separating means includes a condenser arranged between the solid matter separating means and the centrifuge housing, the condenser including: an elongated condenser housing with an intake and outlet for the carrier medium as well as an independent intake and outlet for a coolant fluid; a plurality of substantially vertical coolant pipes of flattened cross-section arranged inside the condenser housing, the carrier medium passing horizontally between the vertical coolant pipes; and a vertical separator lip at the downstream extremity of each coolant pipe, the separator lip having a curved profile to catch the droplets of condensate forming in the passing carrier medium.
 9. The device as defined in claim 8, wherein the coolant pipes are arranged in groups of parallel pipes with flow channels therebetween, the pipe groups being mounted in upper and lower pipe panels located at a distance from the respective condenser housing walls; the condenser further including baffle panels arranged alternately between the upper and lower pipe panels and the adjacent condenser wall, thereby causing an alternately rising and falling flow of coolant through the successive groups of coolant pipes.
 10. A method of discharging and processing the solvent-prepared solid matter from a drum centrifuge including the steps of: scraping from the centrifuge drum a thin layer of solid matter; passing a hot stream of carrier gas through the centrifuge to convey the scrapings of solid matter out of the centrifuge; drying the solid matter during conveyance through evaporation of its solvent residue; collecting the dried solid matter from the flowing carrier gas; and cooling the mixture of solvent vapor and carrier gas to reclaim the solvent as condensate. 